1. Field of the Invention
The present invention relates to an apparatus used for suppressing or preventing an image blur generated due to, e.g., a hand shake.
2. Related Background Art
Conventionally, video cameras and still cameras, each of which has an image blur prevention function for preventing an image blur caused by a hand shake upon photographing, have been proposed, and some video cameras are commercially available.
As an image blur prevention apparatus (to be referred to as a blur prevention control apparatus hereinafter) for preventing an image blur even when a camera vibrates upon photographing, various systems of apparatuses (for example, a system of changing the focusing position by deflecting a transmission light beam by displacing some lenses in a photographing optical system) have been proposed.
The conventional blur prevention control apparatus for a camera has the following practical problems to be solved. The relationship between the type of camera and the blur prevention control apparatus will be explained below to clarify these problems.
When a photographer takes a picture of an objects he or she selects the ON or OFF state of the blur prevention control apparatus by systematically discriminating the focal length and shutter speed of the camera and a hand shake state by himself or herself via a finder. For example, even when the focal length is as large as 300 mm, and a hand shake via the finder is conspicuous, if the shutter speed is as high as 1/500 sec, the blur prevention function is not required. On the other hand, even if the focal length is as small as about 100 mm, and a hand shake is not conspicuous, if the shutter speed is as low as 1/60 sec, the blur prevention function is required since a blur is recorded on an image plane.
In other words, the photographer is required to have the capability of instantaneously selecting the ON/OFF state of the blur prevention control apparatus on the basis of various kinds of information.
Thus, a conventional camera with an image blur correction or compensation apparatus has switching or selection means for switching the active or inactive state of the image blur correction apparatus As one of the switching or selection methods, the assignee of the present applicant discloses a method of selecting the active or inactive state of the image blur correction apparatus by a photographer using a special-purpose switch (to be referred to as a manual switching method hereinafter) in, e.g., Japanese Laid-Open Patent Application No. 4-95933. In the camera of this proposal, a switch for selecting the active/inactive state of an image blur correction function is provided to an exchangeable lens of a single-lens reflex camera. When the switch is set at an active position by a photographer, the image blur correction function is activated in response to the ON operation of a first stroke switch of a release button.
However, this switching operation is very troublesome for normal users. On the other hand, recent cameras tend to have many operation switches. With such a tendency, it is not preferable for users to add another switch for a blur prevention function.
Of course, if the blur prevention function is activated in all photographing states, the above-mentioned problem will not be posed. However, when the blur prevention function is always activated, quick consumption of a battery poses another problem.
In the above-mentioned manual switching method, once the active/inactive state of the image blur correction function is set, the active/inactive state of the image blur correction function cannot be quickly switched if it is required to instantly switch the image blur correction function, and a photographing operation must be temporarily interrupted.
When the blur prevention control apparatus is applied to a single-lens reflex camera in which a lens is detachable from a Camera body, a hand shake state can be easily found since most single-lens reflex cameras have high finder magnifications. Furthermore, since the shutter speed is displayed inside or outside the finder, skilled photographers can select the ON/OFF state of the blur prevention control apparatus based on such information, as described above.
However, necessity of the blur prevention function is not limited to such single-lens reflex cameras, and the blur prevention control apparatus must be equipped in cameras such as compact cameras, which can be easily operated. However, when the above-mentioned known apparatus is equipped in a compact camera, the following problems must be solved.
In general, most compact cameras have finder magnifications lower than that of single-lens reflex cameras, and hence, a hand shake state caused by a photographer himself or herself is not easily found. Furthermore, in most compact cameras, the shutter speed is not displayed. Therefore, the criterion of discrimination of the ON/OFF state of the blur prevention control apparatus in a compact camera is only the focal length and an environmental brightness (the shutter speed is discriminated based on the environmental brightness), and a photographer may unexpectedly take a blurred picture without activating the blur prevention function in a situation wherein the blur prevention control apparatus must be turned on to perform a photographing operation.
As another conventional method of switching or selecting the active or inactive state of the image blur correction function, some methods of activating the image blur correction function when a camera determines the necessity of the image blur correction function (to be referred to as an automatic switching method hereinafter) have been proposed. For example, in Japanese Laid-Open Patent Application No. 4-56831 proposed by the present applicant, a detected image blur amount is compared with a predetermined value, which is set in advance, and if the image blur amount is smaller than the predetermined value, the image blur correction function is automatically inactivated. Also, in the proposal of Japanese Laid-Open Patent Application No. 2-181741, if it is recognized that a camera is fixed to a tripod, the image blur correction function is inactivated.
However, with the automatic switching method, when a switching operation against a photographer's will is made, it cannot be stopped. More specifically, the active/inactive state of the image blur correction function is solely determined by the camera, and the photographer's will cannot be reflected.